This invention relates to ultrasonic imaging systems with provision for measuring the velocity of liquid flow, and more particularly to satisfying the different bandwidth requirements of duplex systems having a common transducer array so as to realize optimum performance in either modality.
B-scan imaging systems for medical diagnostic examination produce a two-dimensional visual image of a planar slice through the human body, and are designed to offer optimum resolving power and contrast between tissue interfaces at dimensions comparable to the illuminating wavelengths. Ultrasound Doppler systems require information relating to blood flow velocity by detecting the frequency shifts imparted to ultrasound by reflection from moving red blood cells, and have the objective of providing adequate blood velocity discrimination over a certain range. Thus, B-scan images require broad band transducers for high resolution and Doppler systems on the other hand require narrow band transducers in order to provide accurate velocity readings. If the same transducer is to be used in a duplex system there is the problem of a conflicting bandwidth requirement.
Advances in imaging techniques have made a significant impact in the diagnosis of cardiovascular disease by improving medical science's ability to define structural disorders in the heart and great vessels. The ability would be greatly enhanced by developing sophisticated equipment for detecting abnormalities in blood flow in the arterial vessels and through the heart valves and cardiac chambers. Several methods for sensing blood flow parameters are known, but despite recent progress there still remains a need for a detection scheme that is safe, yields accurate data, and derives data rapidly enough to reflect variations occurring in the course of a heart cycle. The diagnostic value of such a scheme is vastly improved when combined with a suitable imaging technique so that the physician can determine the precise location in the blood stream from which data is reported. The use of a common transducer for B-scan and Doppler modes has advantages in the accuracy of orientation of the transmitted acoustic beam in the latter case and in system simplicity.
A currently available duplex ultrasound system utilizes a separate transducer for the B-scan and Doppler functions. In alternative implementations, involving a common transducer, the performance during imaging is compromised in order to obtain some frequency shift and velocity measuring facility. The object of this invention is to satisfy the conflicting transducer bandwidth requirements with minimum additional system complexity and without sacrifices in performance in either modality.